1. Technical Field of the Invention
The present invention relates to a hand tool for grinding the surface of an object with an abrasive sheet carried by the tool body, and particularly to a hand tool comprising a tool body including a generally flat surface and a cushion member having a first surface secured to the flat surface of the tool body and an opposite generally flat attachment surface on which an attachment means-backed (e.g., pressure-sensitive adhesive-backed) abrasive sheet may be detachably attached.
2. Description of the Related Art
Abrasive hand tools used for the grinding or surface-finishing of wooden or metallic objects are well-known in the art. Certain types of such tools generally have a small size and are of a light weight sufficient for use by a single hand of the operator, while detachably mounting thereon an abrasive sheet of a desired abrasive particle size. The abrasive sheet typically has abrasive particles on the front surface of a backing and a coating of attachment material such as pressure-sensitive adhesive capable of repeated attachment to and detachment from the tool on the back surface. An adhesive-coated abrasive sheet is preferred in view of its excellent performance with such a tool.
In general, the tool body of the abrasive hand tool of this type is formed of a relatively rigid material for the purpose of transmitting the pressure from the operator's hand to the abrasive sheet. In such a case, a structure is advantageously employed, wherein a thin sheet-like cushion member of a resinous material is permanently secured to a generally flat bearing surface of the tool body and the abrasive sheet with the pressure sensitive adhesive is detachably attached to a generally flat attachment surface of the cushion member. Such a cushion member provides a smooth surface for the abrasive sheet during grinding and reduces user fatigue.
The cushion member used in prior commercial abrasive hand tools generally consists of an inner or first layer of a foam typically permanently bonded by adhesive to the bearing surface of the tool body and a sheet-like outer or second layer bonded to the inner layer also with adhesive. The inner layer has a cushioning function for improving the surface smoothness and reducing user fatigue, and is generally made of polyurethane foam. The outer layer has an attachment surface for holding the abrasive sheet and has sufficient structural integrity to permit detachment (replacement) of the abrasive sheet without structural failure. The outer layer is generally made of a polyvinyl chloride sheet.
Since the inner and outer layers of the cushion member are typically made of different polymeric materials, they have different thermal expansion properties in use as heat is transmitted from the abrasive sheet to the cushion member during the grinding operation. As a result, the outer layer is relatively easily separated from the inner layer particularly in the peripheral area thereof, because of the frictional force encountered during the grinding operation. Such a separation is particularly noticeable when the adhesive provided between the inner and outer layers is insufficiently cured or if the adhesive tends to be softened by heat. If the abrasive sheet is attached to the cushion member in which such a separation has occurred, it becomes difficult to hold the abrasive sheet flat to provide the needed smooth grinding surface.
In addition, with the conventional abrasive hand tool, there is a risk that the frictional force and heat generated during the grinding operation may cause failure of the adhesive bond between the foam cushion member surface and the surface of the tool to which it is adhered whereby the cushion member may detach from the tool body.
Moreover, in a conventional abrasive hand tool, the pressure sensitive adhesive of the abrasive sheet coated on the attachment surface of the cushion member may be transferred to the attachment surface because of softening caused by the frictional heat during the grinding operation. If this happens, the transferred adhesive must be removed from the attachment surface when the exhausted abrasive sheet is replaced by a fresh one, in order to maintain the flatness of the attachment surface.
Accordingly, an object of the present invention is to provide a hand tool capable of reducing or preventing the separation of the outer layer from the inner layer of the cushion member which may result from the frictional heat and force generated during the grinding operation.
Another object of the present invention is to provide a hand tool capable of reducing or preventing the detaching of the cushion member from the bearing surface of the tool body which may result from the frictional heat and force generated during the grinding operation.
A further object of the present invention is to provide a hand tool capable of reducing or preventing the transfer of the pressure sensitive adhesive coated on a abrasive sheet to an attachment surface of a cushion member which may result from the frictional heat and force generated during the grinding operation.